Question

include using namespace std; int x; void summer(int&, int); void fall(int, int&); int main() { int intNum1 = 2; … # What is the output of the following program? #include using namespace std; int x; void summer(int&, int); void fall(int, int&); int main() { int intNum1 = 2; int intNum2 = 5; x = 6; summer(intNum1, intNum2); cout << intNum1 << " " << intNum2 << " " << x << endl; fall(intNum1, intNum2); cout << intNum1 << " " << intNum2 << " " << x << endl; return 0; } void summer(int& a, int b) { int intNum1; intNum1 = b + 12; a = 2 * b + 5; b = intNum1 + 4; } void fall(int u, int& v) { int intNum2; intNum2= x; v = intNum2 * 4; x = u - v; }

Short answer

The outputs are `15 5 6` and `15 24 -9`.

Step-by-step solution

Initial Analysis

First, we look at the initial values of the variables: `intNum1` is 2, `intNum2` is 5, and `x` is set to 6 at the beginning of `main()`.

Call to `summer` Function

The `summer` function is called with `intNum1` (passed by reference) and `intNum2` (passed by value). Inside `summer`, `intNum1` is updated to `2 * intNum2 + 5`, which evaluates to `2 * 5 + 5 = 15`. The value of `intNum2` remains unchanged outside the function because it is passed by value. `x` also remains unchanged.

Output After `summer`

The program then outputs the values of `intNum1`, `intNum2`, and `x`. At this point, `intNum1` is 15, `intNum2` is 5, and `x` remains 6. The output is `15 5 6`.

Call to `fall` Function

The `fall` function is called with `intNum1` (passed by value) and `intNum2` (passed by reference). Inside `fall`, `intNum2` is set to `x * 4`, which is `6 * 4 = 24`. Then, `x` is updated to `intNum1 - intNum2`, which is `15 - 24 = -9`.

Output After `fall`

The program outputs the values again. Now, `intNum1` is still 15, `intNum2` is 24 (since it was passed by reference and modified in `fall`), and `x` is -9. Hence, the output is `15 24 -9`.

Key concepts

Pass by Reference

In C++, passing a variable by reference means that you are sending the address of the variable to the function. This allows the function to modify the original variable directly. The syntax involves using an ampersand `&` with the parameter in the function signature. This is particularly useful when you want a function to change the value of a variable that is defined outside of its own scope.

In the provided exercise, when the `summer` function is called, the parameter `intNum1` is passed by reference. Thus, any changes made to `a` inside the function affect the actual `intNum1` variable in the `main` function scope.

• Original `intNum1`: 2
• Inside `summer`: `intNum1` becomes 15 after the calculation.
• This change is reflected outside of `summer` as well, demonstrating the effect of pass by reference.

Pass by reference is also seen in the `fall` function where `intNum2` is passed by reference, allowing `fall` to modify its value to 24, affecting the original variable.

Pass by Value

Passing by value is another C++ method of passing parameters to a function where a copy of the variable's value is made. In this method, the original variable remains unchanged even if you modify the parameter inside the function. It is the standard behavior for arguments in C++ unless specified otherwise.

In the exercise, `intNum2` is passed by value to the `summer` function. Inside `summer`, modifications made to `b` do not affect `intNum2` outside the function. It remains 5 after the function call even if changes occur within the function.

For the `fall` function, the parameter `u` is passed by value. Hence, its real value doesn't change outside the function despite any operations occurring within it. This concept is beneficial when you want to ensure the original data remains intact post function execution.

• Preserves the original variable value outside the function.
• Used when no modification to the original variable is desired.

Variable Scope

Scope in C++ refers to the visibility and lifetime of variables. Simply put, it determines where a variable can be accessed or modified within the code. Variables can have local scope if they are declared inside a function or block, or global scope if declared outside.

In the given exercise, several variables demonstrate the principle of variable scope:

• `int x` has global scope as it is declared outside any function, making it accessible and modifiable throughout the program.
• Local variables such as `intNum1` inside `summer` cannot affect global or other function variables. They're confined to their specific block.

Understanding and managing variable scope is key to avoiding conflicts and unexpected results in program execution.

Function Parameters

In C++, function parameters distinguish what data will be received by the function. Parameters can be given different types like `int`, `float`, and others, and can also specify whether the data is to be passed by reference or by value.

In our exercise, the `summer` function takes two parameters: one with `int&` indicating pass by reference, and another regular `int` suggesting pass by value. This allows `summer` to modify `intNum1` but not affect `intNum2`, preserving its original value outside the function.

The `fall` function reverses this by taking `int` and `int&` types, thus modifying `intNum2` but not affecting `intNum1` outside. It is crucial to consider the function parameter type to correctly predict how the function will interact with the given data.

• Parameters dictate function interaction with data.
• Determine if functions may alter original variables.